In situ growth of hierarchical NiO microspheres via ionic liquid-assisted synthesis for ppb-level detection of H2S

Well-defined hierarchical NiO microspheres were in situ deposited on ceramic tubes by a simple ionic liquid (IL)-assisted solvothermal method with subsequent calcination, and the characterization was exclusively confirmed through XRD, SEM, TEM and nitrogen adsorption-desorption techniques. Morphological characterization demonstrated that the nanostructures were constructed of interlaced porous nanosheets. Such NiO microspheres in situ grew onto ceramic tubes to form deposited film sensors, which displayed enhanced H2S sensing properties compared with the coated film sensors painted with the powder prepared in the same reaction system. Specifically, the deposited film sensor achieved a response value of 154.2–100 ppm H2S at a low working temperature of 92 °C, a fast recovery time of 7.5 s, with the lowest detection limit of 0.1 ppb. The excellent sensing performance should be attributed to the superior reactivity of the porous hierarchical architecture with large specific surface area, which facilitated the gas molecules to adsorb onto the surface and the consequent electron transfer. The reaction mechanism of the sensor to H2S was also discussed in detail based on XPS analysis, and was eventually interpreted as the two different kinds of kinetics occurring simultaneously: the oxidation of H2S molecules by chemisorbed oxygen, and the NiS formation along with the reaction of H2S with NiO.